http://www.adafruit.com/product/1601
This leaves a few gpios unused. Details on the link. It shouldnt be a problem to add buttons, the gpio seems diesgned to add digital buttons pretty easily. You can use a multiplexor to add as many buttons as youd like:
http://chester.me/archives/2014/08/conn … pberry-pi/
The gp2x suffers against the psp for a few reasons:
- fake dpad
- shitty battery life
- (arguably) lower quality sound
- no suspend to ram feature
- i think the shoulder buttons feel better.
- built in wifi lets you grab samples from the world.
- bulti in mic on newer modules lets you sample (but with the hassle of having to use a file manager.
My dream handheld would include the above, but with the midi and usb audio capabilities of the pi, along with maybe a boot menu switch that lets you boot into a simple audio recorder for on the go sampling. Another button can be used for rsyncing your project folder to the cloud 
.
